Tens of thousands of people joined one of the biggest global days of climate change activism on Sunday, from Sydney to Berlin, to put pressure on world leaders to unite in fighting global warming at a summit in Paris.

About 20,000 pairs of shoes were laid out in the Place de la Republique in the French capital, from high-heels to boots, to symbolise absent marchers after attacks by Islamic State militants killed 130 people on Nov. 13 and led France to ban a protest that was meant to be at the heart of the global action.

Organisers said the Vatican sent a pair of shoes on behalf of Pope Francis. One activist, dressed in white as an angel with large wings, held a sign saying "coal kills".

More than 2,000 events were being held in cities including Sydney, Berlin, London, Sao Paulo and New York, making it perhaps the biggest day of climate action in history on the eve of the Paris conference which runs from Nov. 30-Dec. 11.

ReutersThe capitals of the world's two most populous nations, China and India, were blanketed in hazardous, choking smog on Monday as climate change talks began in Paris, where leaders of both countries are leading participants.

by elizabeth.culliford11/30/2015 8:41:13 AM

Delegates take a break during the opening day of the World Climate Change Conference 2015 (COP21) at Le Bourget, near Paris, France, November 30, 2015. REUTERS/Jacky Naegelen

by Reuters_LindaNoakes11/30/2015 8:42:00 AM

Costly 'cleaner' coal fights for space in emissions debate

The global coal industry is trumpeting "cleaner coal" technology to fight bubbling competition from renewable energy, but the high costs of greener plants are proving a major obstacle in selling them to power-hungry countries such as India.

The challenges are highlighted by the experience of Japan - despite a concerted push by Tokyo to take a lead in exporting the technology, only 7 percent of the power stations built or planned since 2010 with funds from Tokyo's export credit agency were of the most energy-efficient type, according to data from a group of NGOs.

Senior negotiators from almost 200 nations on Sunday began thrashing out a new global deal to curb climate change as the president of China, the world's biggest polluter, landed in Paris.

The United Nations conference begins at summit level on Monday, when more than 150 heads of state and government - including U.S. President Barack Obama and Chinese President Xi Jinping - will attend talks at a sprawling complex north of the French capital. Xi arrived on Sunday.

To signal determination to resolve the most intractable issues, expert negotiators sat down on Sunday rather than after Monday's high-level speeches, as originally planned.

French Foreign Minister Laurent Fabius said the aim was to give the world the means to cap global warming at 2 degrees Celsius (3.6 degrees Fahrenheit) above pre-industrial times or even 1.5 degrees.

That would avoid the most devastating consequences of global warming, such as rising sea-levels and desertification.

Referring to previous U.N. conferences that have dragged on days beyond the official close, Fabius said relying on "a last-night miracle" could risk failure. Progress must be made every day.

People take part in a protest about climate change around New York City Hall at lower Manhattan, New York, November 29, 2015, a day before the start of the Paris Climate Change Conference (COP21). REUTERS/Eduardo Munoz

An environmentalist reacts in front of French CRS police near the Place de la Republique after the cancellation of a planned climate march following shootings in the French capital, ahead of the World Climate Change Conference 2015 (COP21), in Paris, France, November 29, 2015. REUTERS/Benoit Tessier

A protester dressed in police uniform takes part in a protest about climate change around New York City Hall at lower Manhattan, New York, November 29, 2015, a day before the start of THE Paris Climate Change Conference (COP21). REUTERS/Eduardo Munoz

Pairs of shoes are symbolically placed on the Place de la Republique, after the cancellation of a planned climate march following shootings in the French capital, ahead of the World Climate Change Conference 2015 (COP21), in Paris, France, November 29, 2015. REUTERS/Eric Gaillard

An activist takes part in a rally held the day before the start of the Paris Climate Change Conference (COP21), in San Jose, Costa Rica, November 29, 2015. REUTERS/Juan Carlos Ulate

Demonstrators clash with CRS riot policemen near the Place de la Republique after the cancellation of a planned climate march following shootings in the French capital, ahead of the World Climate Change Conference 2015 (COP21), in Paris, France, November 29, 2015. REUTERS/Eric Gaillard

Indigenous children depict fish in the sea during a rally held the day before the start of the Paris Climate Change Conference (COP21), in Sao Paulo, Brazil, November 29, 2015. REUTERS/Nacho Doce

Protesters lie next to signs reading "I am the Doce river" during a rally held the day before the start of the Paris Climate Change Conference (COP21), in Rio de Janeiro, Brazil, November 29, 2015. REUTERS/Pilar Olivares

Protesters take part in a rally held a day before the start of the 2015 Paris Climate Change Conference (COP21), on Parliament Hill in Ottawa, Canada, November 29, 2015. REUTERS/Chris Wattie

More than half a million people from Australia to Paraguay joined the biggest day of climate change activism in history on Sunday, telling world leaders gathering for a summit in Paris there is "No Planet B" in the fight against global warming.

In the French capital, where demonstrations were banned by the authorities after attacks by Islamic State militants killed 130 people on Nov. 13, activists laid out more than 20,000 shoes in the Place de la Republique to symbolize absent marchers on the eve of the summit.

Among the high heels and sandals were a pair of plain black shoes sent by Pope Francis, who has been a vocal advocate for action to prevent dangerous climate change, and jogging shoes from U.N. Secretary-General Ban Ki-moon.

French Ecology Minister Segolene Royal (C) welcomes Britain's Prince Charles (R) as Secretary of the UN Framework Convention on Climate change Christiana Figueres (L) looks on for the opening day of the World Climate Change Conference 2015

by Reuters_LindaNoakes11/30/2015 8:55:44 AM

Delegates are taking their seats for the opening statements at #COP21 - we are watching a feed into a… instagram.com

A voice-over host in the main room for the plenary is asking 'Distinguished delegates and guests' to please take their seats again. No matter how important, organizing a big group of people is never easy...

by jamillah.knowles11/30/2015 9:03:05 AM

More firmly and with fewer niceties the voice over lets us all know that proceedings will begin in two minutes.

by jamillah.knowles11/30/2015 9:04:39 AM

The conference is declared open with pleasure. And speakers head to the main lectern to give their opening comments.

by jamillah.knowles11/30/2015 9:07:12 AM

Meanwhile, outside more delegates are still arriving and are welcomed on a suitably green carpet. Each one is turning up in the usual black car that dignitaries travel in, with flags of their nations on the bonnet.

by jamillah.knowles11/30/2015 9:09:58 AM

U.S., China agree to push for climate change deal in Paris

U.S. President Barack Obama and Chinese counterpart Xi Jinping pledged on Monday to work together to drive forward a climate change agreement at international talks in Paris.

Ahead of a bilateral meeting with Xi, Obama said the leadership of the two countries was critical in pushing participating countries to cut emissions.

More than 150 world leaders arrived at United Nations climate change talks in Paris armed with promises and accompanied by high expectations as they look to hold back the Earth's rising temperatures.

BARCELONA Spain mounted a sweeping anti-terror operation on Friday after a suspected Islamist militant drove a van into crowds in Barcelona, killing 13 people before fleeing, in what police suspect was one of multiple planned attacks. | Video

Reuters, the news and media division of Thomson Reuters, is the world’s largest international multimedia news provider reaching more than one billion people every day. Reuters provides trusted business, financial, national, and international news to professionals via Thomson Reuters desktops, the world's media organizations, and directly to consumers at Reuters.com and via Reuters TV. Learn more about Thomson Reuters products: